1. Field of the Invention
This invention generally relates to circuit interrupter apparatus and, more particularly, to an improved trip-actuating assembly for a molded case type circuit breaker that is designed for shipboard use and is thus subjected to mechanical shocks and vibrations of unusual severity.
2. Description of the Prior Art
Circuit breakers and related electrical generation and distribution equipment for shipboard use require special design features insofar as they must operate under adverse environmental conditions characterized by high humidity, salt water spray, high ambient temperatures, high vibration levels and high mechanical shock loads. As will be appreciated by those skilled in the art, reliable operation of the electrical equipment under such adverse operating conditions is very difficult to achieve, particularly with regard to the requirement that the equipment be able to withstand mechanical shocks and impacts. This is of special importance in the case of naval vessels that frequently experience shocks and vibrations of very high magnitude during combat when operation of the electrical system is most crucial and difficult. Various modifications to the electrical equipment intended for shipboard use have accordingly been developed over the years to render it shock-proof. However, these modifications not only increased the cost of the apparatus but complicated its manufacture on a mass production basis. Such drawbacks are of even greater significance in the design and marketing of molded case circuit breakers which are traditionally low cost, compact devices that are inherently sensitive to mechanical shocks and impacts. The need to instantly trip on high currents makes the trigger mechanism of such breakers sensitive to shock loads while the compact designs and low cost make it very difficult to provide a cost-effective reliable shock-resistant tripping mechanism in the available space within the breaker case.
A shock-resistant trip device currently used in commercial circuit breakers of the molded case type utilizes a rotatable trigger component that has a protruding latch which engages a slidable release member and holds the spring-loaded tripping mechanism of the circuit breaker in contact-closed position. The rotatable trigger component is spring biased to keep it in latched relationship with the release member and the trigger component is actuated by a magnetic trip device consisting of an electromagnet that is energized when a current overload condition is created by a fault or some other malfunction in the electric circuit being protected. The electromagnet attracts a pivoted clapper that has an end portion which engages a protruding tab-like portion of the rotatable trigger component and moves the trigger component a sufficient distance against the action of the biasing spring that the trigger latch is disengaged from the release member--thus permitting the cocked driving springs and toggle assembly of the breaker mechanism to slide the release member in a direction which allows the trip mechanism to open the breaker contacts and quickly interrupt the circuit. In accordance with standard design practice, the circuit breaker is restored to contact-closed position by a manual or motor operated closing sequence which extends or compresses suitable springs in the trip mechanism and stores the energy required for the next trip operation. The springs are prevented from tripping the circuit breaker by the slidable release member which, in turn, is controlled by the rotatable trigger component and its latch.
While such shock-resistant tripping mechanisms are in widespread use in commercial type molded case circuit breakers and function satisfactorily, they are not suitable for use in circuit breakers installed on naval vessels since the severe shock loads encountered aboard such vessels are sufficient to actuate the triggering mechanism and cause the breaker to be tripped from mechanical as well as electrical loads. Since the shock loads are most intense during combat the accidental tripping of circuit breakers under such conditions is intolerable since it deprives the ship of electrical power when it is most needed.
In order to make the aforementioned prior art tripping mechanism less sensitive to mechanical shocks and impacts inertia wheels were added to the mechanism to prevent the trigger component from reacting to high frequency mechanical loads. The inertia wheels were coupled to the rotatable trigger component in such a way that they prevented the rapid acceleration of the trigger component and thus helped to isolate the trigger component from impulse-type shock loads. While this arrangement improved the shock tolerance of the tripping mechanism, it was not "fail safe" and it is relatively ineffective for high amplitude, low frequency shock loadings of the kind that would be encountered aboard naval vessels.
It would, accordingly, be very advantageous from both a functional and marketing standpoint if a circuit breaker could be provided with a shock-proof triggering device that was compact, reliable, low in cost and geometrically flexible enough to be easily adapted to the available space in the molded case breakers now being manufactured and marketed and thus produce circuit breakers of this type that have the operational stability and ruggedness required for shipboard use and similar rough service applications.